A damping device is normally used to damp the vibration of the structure. For instance, Patent Literature 1 discloses a vibration control apparatus having a damping unit of an inverted pendulum type. The vibration control apparatus includes a weight mass, a rod which is installed upright to support the weight like an inverted pendulum, a supporting member which supports the middle part of the rod as a supporting point of the inverted pendulum, a drive unit which moves a lower end of the rod in a desired direction and a spring whose one end is connected to the rod and whose other end is connected to an object whose vibration is controlled.
For instance, another vibration control apparatus is described in Patent Literature 2. The vibration control apparatus includes a pendulum damping unit and an inverted-pendulum damping unit. The pendulum damping unit has a first weight suspended from the top of the object to be controlled. The inverted pendulum dumping unit has a second weight supported by a rod installed upright on the bottom of the object. The first and second weight are freely movable in a vertical direction and are interlocked by a connection member for moving the first and second weights in conjunction in a horizontal direction.
Yet another vibration control apparatus is described in Patent Literature 3. The vibration control apparatus includes an inverted-pendulum damping unit and a rotation damping unit utilizing rotatory inertia. The inverted-pendulum damping unit is installed upright on the bottom of the object to support a weight by a multiple layers of laminated rubbers. The rotation damping unit has a shaft which rotates while moving in a horizontal direction in conjunction with a movement of a weight unit having a plurality of weights connected thereto, a cable winded around the shaft and a cable mount to which both ends of the cable are connected via a linear guide.